This work investigates the effect of polymer molecular weight (M-w) on the morphological and chemical modifications and on the plume ejection of doped polymethyl methacrylate (PMMA), and polystyrene (PS) films following irradiation at 248 nm. Micro-bubbles develop in the irradiated films of the low absorbing PMMA-based substrates. The extent and kinetics of the observed morphological changes are respectively larger and last longer in the low M-w polymer, as evidenced by optical microscopy and real-time monitoring of transmission of a CW laser. The changes observed in the Raman spectra upon irradiation indicate that degradation occurs to a higher extent in larger M-w polymers. Laser induced fluorescence (LIF) probing of the plume reveals the presence of NapH and PhenH products from, respectively, NapI- and PhenI-doped films and a slower ejection process in the plume of low M-w polymer. For highly absorbing PS, a less dramatic dependence on M-w is observed. Results are discussed in the framework of the bulk photothermal model, according to which ejection requires a critical number of bonds to be broken. (c) 2007 Elsevier B.V. All rights reserved.